1 The current situation of hard tooth surface grinding processing In recent years, the rapid development of the equipment manufacturing industry, the number of imported forming gear grinding machines in the country has increased greatly, which has significantly improved gear machining precision and machining efficiency. However, some problems of forming the grinding teeth are also exposed. The most important thing is that the root of the tooth groove after grinding is released, which destroys the arc of the root of the gear and the transition curve. The stress concentration at the root of the gear reduces the strength of the tooth portion.
The problem of the introduction of the root of the gear, the analysis of the relevant personnel of our company, the main factors are:
1) The amount of root cutting of the hob before grinding is small.
2) The depth of cut is too large when forming the grinding teeth. In order to eliminate the above two main factors, reduce and eliminate the problem of rooting after forming the grinding tooth, you can take:
(1) Increase the amount of root undercut, but the side effect is that the effective meshing length of the gear is reduced, and the gear meshing coincidence is reduced;
(2) Determine the available root circle diameter based on the actual meshing point of the mating gear mesh. To balance these two measures, the root cutting amount should be increased under the premise of ensuring the effective meshing length of the mating gears, and the root diameter of the forming grinding teeth can be determined, and the radius of the root arc can be increased as much as possible to improve the root strength. And gear, transmission accuracy.
2, as shown by the meshing line 1 of the gear transmission, when a pair of involute tooth profiles are engaged at any point B, the common normal line N1N2 of the pair of tooth profiles passing the point B is an inner common tangent of the two base circles. Since the two base circles are in a fixed circle and there is only one inner common tangent line in the same direction, the pair of tooth profiles can be engaged at any position, and the common normal line of the two tooth profiles of the over meshing point P must coincide with the inner common tangent line N1N2, that is, one For the involute tooth profile from the beginning to the disengagement, all the meshing points are on the inner common tangent line N1N2, so the common tangent line N1N2 is called the meshing line.
3 The involute profile can ensure that the meshing line of the pair of involute profiles is a straight line with a fixed gear ratio, and the intersection P with the connecting line O1O2 must be a certain point; therefore, the involute profile can be realized. Fixed transmission ratio transmission.
4 Paired gear meshing can be calculated from the diameter of the root circle. The diameter of the involute spur gear meshing start circle refers to the diameter of the circle where the pair of gears are engaged when the meshing drive is engaged. The available gear root of the gear meshing transmission is effective after considering the centering distance adjustment when the gear is installed and the gear is warmed up due to the temperature rise and the gear is warmed up on the basis of the gear meshing starting circle. Involute starting circle diameter.
1: 1) Set gear O1: base circle radius rb1, top circle radius ra1, pitch circle pressure angle α', top circle pressure angle αa1, then root engagement initial circle pressure angle αB1; 2) set gear O2: The base circle radius rb2, the top circle radius ra2, the pitch circle pressure angle α', and the top circle pressure angle αa2, the tooth root meshes with the starting circle pressure angle αB2.
Now, according to the end face modulus mt, the end face pressure angle αt, the starting circle algorithm of the tooth root operation is introduced: (1) The end face modulus is: mt=mn/cosβ.
Where mn is the normal modulus. (2) The end face pressure angle is: tgαt = tgαncosβ.
Where αn is the normal pressure angle. (3) The diameter of the base circle is: db=2rb1=mtZ1cosαt where db is the diameter of the base circle. (4) Conjugate gear meshing angle (α): cosα = cosα' = 0.5mtZΣcosαt/a.
Where Z is the sum of the number of teeth of the mating gears and a is the center distance.
5) Tip circle diameter: da = mtZ 2mn (1 X).
Where Z is the number of teeth and X is the coefficient of displacement. (6) Tip crown pressure angle: cosαa=rb/ra=db/da.
Root root engagement end pressure angle (αB): tgαB1 = taα - (Z2 / Z1) (tgαa2-tgα). tgαB2=taα-(Z1/Z2)(tgαa1-tgα).
(8) Root diameter of the starting point of the tooth root: dB=db/cosβ.
(9) Available root diameter: Considering the adjustment of the center distance when the gear is installed and the temperature increase due to the gear operation, according to the long-term practical experience of our factory and the external drawings, the available diameter of the root diameter can be used for statistical analysis. Circle diameter = dB-0.05mn.
5 At the end of this paper, based on the principle of gear meshing and hard tooth surface gear machining, the influence of the tooth root circle on the gear work and the design of the actual tooth blank machining, forming gear grinding and the tool blank machining tool are briefly discussed. effect. In order to meet the gear meshing transmission requirements of the design drawings, the accuracy of the carburizing and quenching hard tooth surface gear blanks is improved, and the precision of the carburizing and quenching hard tooth surface gear grinding teeth is ensured, which should be sufficient in the design of the gear hob before grinding. Considering the diameter of the root diameter of the gear meshing, according to the diameter of the tooth root and the level of the heat treatment process, it is an important issue that is worthy of attention to determine the amount of grinding of the pre-grinding gear hob and the hob arc of the hob.
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