Machining Process Analysis of Gear Shaft - Selection of Positioning Reference
Release time:
2023.03.09
Article source:
network
The machining sequence of the main surfaces of the gear shaft largely depends on the selection of the positioning reference. The structural characteristics of shaft parts themselves and the positional accuracy requirements of each main surface of the spindle determine that using the axis as a positioning reference is the most ideal. This not only ensures the unification of the datum, but also makes the positioning datum coincide with the design datum. Generally, the outer circle is used as the coarse reference, and the tip hole at both ends of the shaft is used as the fine reference. The following points should also be noted during specific selection.
(1) When the accuracy requirements for the mutual position between the machined surfaces are high, the machining of each surface is completed in a single clamping process.
(2) When rough machining or positioning with two end center holes (such as machining spindle taper holes) is not possible, in order to improve the rigidity of the process system during workpiece processing, only the outer circular surface can be used for positioning or the outer circular surface and one end center hole can be used as the positioning reference. During the machining process, the outer circle of the shaft and the center hole at one end should be alternately used as the positioning reference to meet the mutual position accuracy requirements.
(3) If the shaft is a part with a through hole, the original center hole will disappear after the through hole is drilled. In order to still be able to position with a center hole, a cone plug or cone sleeve mandrel with a center hole is generally used. When the taper of the shaft hole is large (such as the spindle of a milling machine), a taper sleeve mandrel can be used; When the taper of the spindle taper hole is small (such as the CA6140 machine tool spindle), a cone plug can be used. It must be noted that the taper sleeve mandrel and taper plug used should have high accuracy and minimize their installation times. The central hole on the cone plug or cone sleeve mandrel is not only the positioning reference for its own manufacturing, but also the finishing reference for the outer circle of the main shaft. Therefore, it is necessary to ensure that the cone surface on the cone plug or cone sleeve mandrel has a high coaxiality with the central hole. For medium and small batch production, the workpiece is generally not replaced halfway after installation on the cone plug. If the outer circle and the taper hole need to be repeatedly processed with each other as a reference, it is necessary to align or regrind the center hole according to the outer circle when reinstalling the taper plug or shaft sleeve mandrel.
From the above analysis, selecting the positioning reference during the gear shaft machining process should consider arranging the process as follows: first, use the outer circle as the rough reference to drill the center hole of the end face, and prepare the positioning reference for rough turning; Rough turning of the outer circle prepares a positioning reference for subsequent processing. Thereafter, in order to prepare a positioning reference for semi finishing and finishing of the outer circle, the front and rear center holes are first processed as positioning reference; The machining of gear teeth also uses the center hole as the positioning reference, which very well reflects the principle of unified reference and fully embodies the principle of overlapping reference.
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