The processing sequence of the major surfaces of the gear shaft largely depends on the choice of positioning reference. The structural characteristics of the shaft parts themselves and the positional accuracy requirements of the major surfaces of the main shaft all determine that the axis is the most ideal positioning reference. This will not only ensure the unity of the benchmark, but also align the positioning reference with the design reference. Generally, the outer circle is a rough reference, and the projected holes at both ends of the shaft are the fine references. When making specific choices, please also pay attention to the following points.
(1) When the positional accuracy between the machining surfaces is required to be high, it is better to complete the machining of each surface in one clamping.
(2) For rough machining or when positioning at both ends of the top hole (such as machining spindle taper hole), in order to improve the rigidity of the processing system when the workpiece is processed, only the outer circle surface can be used or the outer circle surface and one end center hole can be used as positioning Benchmarks. During the machining process, the outer circle of the shaft and the center hole at one end should be used alternately as a positioning reference to meet the mutual position accuracy requirements.
(3) If the shaft is a part with a through hole, the original hole will disappear when the through hole is drilled. In order to still be able to use the top hole to position, generally used cone plug or cone sleeve mandrel with a top hole. When the taper of the shaft hole is large (such as the spindle of the milling machine), the taper sleeve can be used; when the taper of the taper of the spindle taper is small (such as the spindle of the CA6140 machine tool), the taper plug can be used. It must be noted that the use of taper mandrels and conical plugs should have high accuracy and minimize the number of installations. The center hole on the taper block and the mandrel of the taper sleeve is not only the positioning reference of its own manufacture, but also the precision machining base of the external shaft of the main shaft. Therefore, it must be ensured that the taper or taper on the taper sleeve has a high Concentricity. For medium and small batch production, the workpiece is generally not changed halfway after being installed on the cone plug. If the outer circle and the taper hole are to be machined repeatedly several times, the center hole must be corrected or reground by the outer circle when reloading the taper or sleeve mandrel.
From the above analysis, the selection of positioning reference during the machining process of the gear shaft should consider arranging the process in such a way that the outer circle is used as the coarse reference for drilling the center hole of the end face to prepare the reference for the roughing; the outer diameter of the roughing car is used as the follow-up. Processing preparation positioning reference: After that, in order to prepare the positioning reference for semi-finishing and finishing machining, the front and back top holes are used as positioning references; the top gear hole is also used as positioning reference, which is very good It embodies the principle of unity of the benchmark and fully reflects the principle of benchmark reunification.
Arrangement of heat treatment process
During the entire process of shaft machining, sufficient heat treatment processes should be arranged to ensure the mechanical properties and machining accuracy of the gear shaft and improve the machining performance of the workpiece.
Normally, after the forging of the shaft blank, the normalizing treatment is firstly arranged to eliminate the forging internal stress, refine the crystal grains, and improve the cutting performance during machining.
After the rough processing, the quenching and tempering processing is arranged. In the roughing stage, after roughing, drilling, and other processes, most of the machining allowance of the gear shaft is cut off. In the roughing process, both the cutting force and the heat generation are very large. Under the action of force and heat, the shaft generates a large internal stress, and the internal stress can be eliminated through quenching and tempering, instead of aging treatment, and the required toughness can be obtained at the same time.
After half-processing, all surfaces except the important surface have reached the design dimensions. Only the finishing allowance is left on the important surface. At this time, a partial quenching treatment is arranged on the teeth, so that it can meet the design's hardness requirements and ensure the wear resistance of these surfaces. Subsequent finishing operations eliminate quench deformation.
Processing sequence arrangement
The arrangement of the machining sequence is based on the principle of the base surface first, the rough after the fine, and the principle of the first and the second. For the general parts of the gear shaft, after the center hole is prepared, the outer circle is processed first, and then the other parts are processed, and attention is paid to rough and finish machining separately. In the gear shaft machining process, heat treatment is used as a mark, rough processing before and after quenching and tempering, semi-finishing before quenching, and finishing after quenching. This separation of the stages ensures that the finishing of the main surface is finally carried out without affecting the main surface accuracy due to the stresses of other surfaces.
When arranging the sequence of gear shaft operations, the following points should also be noted.
(1) The tooth profile rough machining of this shaft should be arranged after the semi-finishing of each outer circle of the gear shaft is completed. As a gear shaft, the tooth profile machining is a relatively heavy work in the part processing and the processing difficulty is also relatively large. Processing content, the appropriate processing position to put some, you can improve the positioning of the reference height, and the tooth shape finishing should be arranged in the parts of the outer circle and other surface after all processing, so as to eliminate the heat treatment deformation of the tooth shape of the local quenching .
(2) The processing sequence of the outer surface of the outer circle should first process the large diameter outer circle, and then process the small diameter outer circle so as not to reduce the rigidity of the work piece at the beginning.
(3) The machining of minor surfaces such as keyways on gear shafts should generally be performed after finishing or rough grinding in the outer race or before fine grinding the outer race. If the keyway is milled in front of the finisher, on the one hand, before the finisher, vibrations due to interrupted cutting will not only affect the machining quality but also damage the tool; on the other hand, the dimensional requirements of the keyway are difficult to guarantee. These surface finishes should also not be arranged after the main surface finish grinding so as not to damage the main surface accuracy.
