Hardware knowledge base: "worm"

Ordinary cylindrical worm drive

The tooth surface of a common cylindrical worm (except for the ZK worm) is generally made on a lathe with a straight bladed turning tool. Depending on the mounting position of the turning tool, the tooth profile of the machined worm tooth flanks in different sections is also different. According to different tooth profiles, ordinary cylindrical worms can be divided into Archimedes worm (ZA worm), involute worm (ZI worm), normal straight worm (ZN worm) and cone enveloping cylindrical worm (ZK Worm) and other four. GB10085-88 recommended using ZI worm and ZK worm two. The worm gears and paired worm gear tooth profiles used in the above four types of ordinary cylindrical worm drive are introduced separately.

Archimedes worm (ZA worm) This type of worm, in the plane perpendicular to the axis of the worm (ie, the end face), has an Archimedes spiral with a tooth profile on the plane containing the axis (ie axial teeth). Profile) is a straight line with a tooth profile angle α0=20°. It can be turned on a lathe using a straight blade with a single blade (when the lead angle γ ≤ 3°) or double blades (when γ> 3°). When installing the tool, the top surface of the cutting edge must pass the axis of the worm, as shown in the Archimedes worm. This kind of worm grinding is difficult, and the machining is inconvenient when the lead angle is large.

Normal straight worm (ZN worm) The worm's end face profile is an extended involute, and the normal (NN) tooth profile is a straight line. The ZN worm is also a single-knife or double-knife lathe with a straight blade. The installation of the tool is shown in Fig. <Normal Straight Worm>. This type of worm grinding is also more difficult.

Involute worm (ZI worm) This type of worm has an involute profile, so it is equivalent to an involute cylindrical helical gear with a small number of teeth (the number of teeth equal to the number of worms) and a large helix angle. The ZI worm can be turned on a lathe with two straight blades. The top surface of the blade should be tangential to the base cylinder, with one tool above the worm axis and the other below the worm axis, as shown in the <involute worm>. The tooth angle of the tool should be equal to the base cylindrical helix angle of the worm. This worm can be ground on a special machine.

Cone Enveloping Cylindrical Worm (ZK Worm) This is a non-linear spiral curved worm. It cannot be machined on a lathe and can only be milled on a milling machine and ground on a grinding machine. During machining, the tool rotates around its own axis, in addition to the workpiece's spiral motion. At this time, the enveloping surface of the turning surface of the milling cutter (or grinding wheel) is the spiral tooth surface of the worm, and the tooth profiles on both the II and NN sections are curves. This kind of worm is easy to grind, the precision of the worm is high, and it is widely used.

As for the worm gear pairing with the above-mentioned various types of worm gears, it completely differs depending on the tooth profile of the worm gear. Worm gears are generally machined on a hobbing machine with a hob or **. In order to ensure that the worm and the worm wheel can be properly meshed, the tooth profile of the hob cutting the worm wheel should be consistent with the tooth profile of the worm; the center distance when deep cutting should also be the same as the center distance of the worm drive.