Worm turning tool and installation method
Worm turning tools are specialized tools used to machine worm gear tooth profiles. Their cutting edge shape must precisely match the worm’s tooth profile. Depending on the worm type, commonly used worm turning tools include Archimedean worm turning tools, involute worm turning tools, and normal straight-flank worm turning tools. The cutting edge of an Archimedean worm turning tool is straight in the axial section, with a cutting edge angle equal to the worm’s tooth profile angle (typically 40°), making it suitable for machining ordinary transmission worms. The cutting edge of an involute worm turning tool is ground to an involute profile and is suitable for machining high-precision worms. Normal straight-flank worm turning tools, on the other hand, have a straight cutting edge in the normal section and are suitable for machining multi-start worms. Practice at a machine tool shop has shown that worm tooth profile errors can be controlled within 0.01mm using specialized worm turning tools, far lower than the 0.03mm error achieved with conventional profile cutters.
The material selection for worm turning tools depends on the worm material and machining requirements. When machining steel worms (such as 45 steel and 40Cr), high-speed steel turning tools (such as W6Mo5Cr4V2) are suitable for low-speed finish turning, achieving excellent tooth surface quality, with cutting speeds generally ranging from 10-30 m/min. Carbide turning tools (such as YT15 and YW1) are suitable for high-speed roughing and semi-finishing turning, with cutting speeds reaching 50-100 m/min, making them particularly suitable for mass production. When machining cast iron worms, YG-type carbide turning tools (such as YG8) are recommended for their improved impact resistance and reduced edge chipping. For high-precision worms (such as machine tool feed worms), final machining requires high-speed steel tooling for finish turning or worm grinding to ensure tooth profile accuracy and surface quality. When a precision machinery factory processes 40Cr tempered worms, it uses a YW1 carbide turning tool for rough turning and then a high-speed steel turning tool for fine turning, so that the cumulative error of the worm’s tooth pitch is controlled within 0.02mm/300mm.
The geometric design parameters of worm turning tools must meet tooth profile accuracy requirements. The rake and clearance angles directly impact cutting performance. When machining steel, the rake angle is 10°-15°, and the clearance angle is 6°-10°; when machining cast iron, the rake angle is 0°-5°, and the clearance angle is 5°-8°. The tooth angle is a key parameter of worm turning tools and must be consistent with the tooth angle of the worm. A worm with a 40° tooth angle requires a turning tool with a 40° cutting edge angle. The symmetry error of the cutting edge should be controlled within ±10°, otherwise the worm tooth profile will skew. The tool body must also ensure rigidity, especially when machining multi-start worms and large-module worms. The tool body should be of sufficient thickness and strength to avoid vibration during cutting. A gear factory achieved this by precision-grinding the cutting edge of a worm turning tool, achieving a tooth angle error of ±5°. This results in a uniform meshing clearance between the worm and worm wheel, and an 8% increase in transmission efficiency.
The installation method of worm turning tools is crucial to machining accuracy. During installation, ensure that the tool’s main cutting edge is aligned with the worm’s axis, meaning the tool tip is at the same height as the worm axis. A deviation exceeding 0.1mm will result in increased tooth profile error. For Archimedean worms, the tool axis should coincide with the worm axis, meaning the tool should be installed at a 0° angle. For worms with a normal profile, the tool should be tilted to the worm’s helix angle, with the angle equal to the worm’s helix angle, to ensure the normal profile of the tooth profile remains straight. During tool installation, the tool can be calibrated using a tool setting template. Alternatively, adjustments can be made through trial cutting, where a small amount of tooth profile is first turned, checked using a tooth profile template, and the tool position adjusted based on the deviation. A machine tool repair shop, while repairing a worm, used a dial indicator to calibrate the tool tip height, keeping the height error within 0.02mm. By adjusting the angle using the tool setting template, they successfully restored the worm’s tooth profile accuracy to the original design requirements.
The use and maintenance of worm turning tools must follow standardized procedures. Before use, inspect the cutting edge for sharpness and defects such as chipping and cracks. Sharpen the tool as necessary, maintaining its original geometric parameters. During installation, securely clamp the toolholder to the toolholder, keeping the extended length as short as possible to enhance rigidity. Use ample cutting fluid during machining. Emulsions are recommended for high-speed steel turning tools, while extreme-pressure cutting oils can be used for carbide turning tools to reduce cutting temperatures and tool wear. When machining multi-start worm gears, each spiral must be accurately divided before the next one is machined. The division error should be controlled within 0.01mm, otherwise uneven worm gear tooth thickness will result. The worm turning tool maintenance procedures established by a precision instrument manufacturer require sharpening and calibration of the tool after every 50 worm gears are machined, to maintain a worm gear machining pass rate of over 99%. With the popularization of CNC lathes, the installation and adjustment of worm turning tools have gradually become digitalized. By accurately measuring the tool parameters with a tool setter and inputting them into the CNC system, efficient and precise processing of the worm can be achieved, providing reliable guarantee for the high-quality operation of the mechanical transmission system.
